PROJECT SUMMARY The alveolar region of the mammalian lung is a complex, precisely structured tissue required for the primary functions of the respiratory system, gas exchange and tissue oxygenation. Damage to the alveolar epithelium plays a central role in human lung diseases including Acute Respiratory Distress Syndrome (ARDS), a prevalent, high impact clinical disorder that affects up to 5% of mechanically ventilated patients in the developed world. The mortality rate of ARDS approaches 40%, and the recovery for ARDS survivors is arduous, with a substantial burden of multi-system disability continuing 5 or more years following hospitalization. Critically, while many ARDS survivors recover lung function, a subset of patients develops persistently abnormal pulmonary function, imaging evidence of pulmonary scarring, and pulmonary symptoms even years after ARDS. To date, no data exists regarding the mechanisms that guide ARDS recovery. A key requirement for developing strategies to improve recovery after ARDS and promote lung regeneration is to understand progenitor populations in the lung, and their specific roles in the complex, regionalized nature of regeneration after injury. We have found a distinct group of Wnt-responsive AT2 cells. These cells comprise a distinct progenitor sublineage, which we call AEPs (Axin2+ Alveolar Epithelial Progenitors). AEPs are capable of generating both AT1 and AT2 cells in vivo and in vitro, are stable for 9 months during alveolar homeostasis, and expand rapidly to regenerate a majority of the alveolar epithelium after diffuse alveolar damage. Importantly, we have identified an AEP-enriched cell surface receptor that marks AEPs in both mouse and human lung, which has allowed functional validation of human AEPs as a progenitor lineage. The ability to directly compare AEPs from mouse and human has provided specific insight into possible upstream signals and downstream effectors required for AEP function. The scientific objective of this proposal is to directly evaluate the requirement and role for several such candidate factors in AEP biology during lung regeneration, with a specific emphasis on the combinatorial role of Wnt and Fgf signals in promoting AEP function. The Aims of the proposal are 1) Define the requirement for Wnt signaling in AEP biology during alveolar regeneration and 2) Determine the function of FGFR2 signaling and ETS transcription factors in AEPs. The other crucial objective of this proposal is to provide for a structured, focused training plan to allow the primary investigator to develop an advanced armamentarium of research techniques in regenerative biology and allow for a successful transition to independence.